Question

java.lang.NullPointerException：尝试调用接口方法＆＃39; boolean java.util.List.add（java.lang.Object）＆＃39;在空对象引用上

这是我的文件

Stitle.java

的java

package com.desktop.app;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.KeyEvent;
import android.view.inputmethod.EditorInfo;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import com.android.volley.AuthFailureError;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Stitle extends AppCompatActivity {

    EditText searchtitle;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.stitle);

        searchtitle = (EditText) findViewById(R.id.searchtitle);

        searchtitle.setOnEditorActionListener(new TextView.OnEditorActionListener() {
            @Override
            public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {
                if (actionId == EditorInfo.IME_ACTION_SEARCH) {
                    performSearch();
                    return true;
                }
                return false;
            }
            List<list> productList;

            //the recyclerview
            RecyclerView recyclerView;


            public void onCreate(Bundle savedInstanceState) {
                Stitle.super.onCreate(savedInstanceState);
                setContentView(R.layout.activity_smain);

                //getting the recyclerview from xml
                recyclerView = findViewById(R.id.recylcerView);
                recyclerView.setHasFixedSize(true);
                recyclerView.setLayoutManager(new LinearLayoutManager(Stitle.this));

                //initializing the productlist
                productList = new ArrayList<>();

                //this method will fetch and parse json
                //to display it in recyclerview
                performSearch();
            }

            private void performSearch() {
                String url= "http://192.168.0.136/fyp/stitle.php";
                final RequestQueue requestQueue = Volley.newRequestQueue(Stitle.this);
                StringRequest stringRequest = new StringRequest(Request.Method.POST, url, new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                       // Log.d("Response", response.toString());
                        try {
                            //converting the string to json array object
                            JSONObject array = new JSONObject(response);
                            Log.i("test"," value : " + array.getString("status"));
                            if (array.getString("status").equals("true")){
                                JSONArray jsonArray =array.getJSONArray("search");
                                Log.i("test"," value : " + jsonArray);

                                for (int i = 0; i < jsonArray.length(); i++) {

                                    //getting product object from json array
                                    JSONObject product = jsonArray.getJSONObject(i);

                                    //adding the product to product list
                                    boolean add = productList.add(new list(
                                            product.getInt("isbn"),
                                            product.getString("title"),
                                            product.getString("authors"),
                                            product.getInt("accession"),
                                            product.getString("publisher"),
                                            product.getInt("pubyear"),
                                            product.getInt("pages"),
                                            product.getInt("rak"),
                                            product.getInt("hr"),
                                            product.getInt("vr"),
                                            product.getInt("barcode")

                                    ));

                                }

                            }else{
                                Log.i("test","else error");

                            }



                            //traversing through all the object


                            //creating adapter object and setting it to recyclerview
                            listAdapter adapter = new listAdapter(Stitle.this, productList);
                            recyclerView.setAdapter(adapter);
                        } catch (JSONException e) {
                            e.printStackTrace();
                            Log.i("test",e.toString());
                        }
                        catch (Exception e){
                            Log.i("test",e.toString());
                        }
                        /*if(response.matches(toString())){
                        } else {
                            Toast.makeText(getApplicationContext(), "Unsuccessfull" ,Toast.LENGTH_LONG).show();
                        }*/
                    }

                }, new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        Toast.makeText(getApplicationContext(), "error:" +error.toString() ,Toast.LENGTH_LONG).show();

                    }
                }) {
                    @Override
                    protected Map<String, String> getParams() throws AuthFailureError {

                        Map<String, String> params = new HashMap<>();
                        params.put("Title", searchtitle.getText().toString());

                        return params;
                    }
                };
                requestQueue.add(stringRequest);

            }

        });
    }
}

list.java

的java

package com.desktop.app;


public class list {
    private long isbn;
    private String title;
    private String authors;
    private int accession;
    private String publisher;
    private int pubyear;
    private int pages;
    private int rak;
    private int hr;
    private int vr;
    private long barcode;


    public list(long isbn, String title, String authors, int accession, String publisher, int pubyear, int pages, int rak, int hr, int vr, long barcode) {
        this.isbn = isbn;
        this.title = title;
        this.authors = authors;
        this.accession = accession;
        this.publisher = publisher;
        this.pubyear = pubyear;
        this.pages = pages;
        this.rak = rak;
        this.hr = hr;
        this.vr = vr;
        this.barcode = barcode;

    }


    public long getIsbn() {
        return isbn;
    }

    public String getTitle() {
        return title;
    }

    public String getAuthors() {
        return authors;
    }

    public int getAccession() {
        return accession;
    }

    public String getPublisher() {
        return publisher;
    }

    public int getPubyear(){
        return pubyear;
    }

    public int getPages(){
        return pages;
    }

    public int getRak(){
        return rak;
    }

    public int getHr(){
        return hr;
    }

    public int getVr(){
        return vr;
    }

    public long getBarcode() {
        return barcode;
    }
}

listAdapter

的java

package com.desktop.app;

import android.annotation.SuppressLint;
import android.content.Context;
import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

//import com.bumptech.glide.Glide;

import java.util.ArrayList;
import java.util.List;

    public class listAdapter extends RecyclerView.Adapter<listAdapter.ProductViewHolder> {


    private Context mCtx;
    private List<list> productList  = new ArrayList<>();

    listAdapter(Context mCtx, List<list> productList) {
        this.mCtx = mCtx;
        this.productList = productList;
    }


    @Override
    public ProductViewHolder onCreateViewHolder( ViewGroup parent, int viewType) {
        LayoutInflater inflater = LayoutInflater.from(mCtx);
        @SuppressLint("InflateParams") View view = inflater.inflate(R.layout.slist, null);
        return new ProductViewHolder(view);
    }

    @Override
    public void onBindViewHolder(ProductViewHolder holder, int position) {
        list product = productList.get(position);

        holder.textviewisbn.setText(String.valueOf(product.getIsbn()));
        holder.textviewtitle.setText(product.getTitle());
        holder.textviewauthors.setText(product.getAuthors());
        holder.textviewacc.setText(String.valueOf(product.getAccession()));
        holder.textviewpublisher.setText(product.getPublisher());
        holder.textviewpubyear.setText(String.valueOf(product.getPubyear()));

    }

    @Override
    public int getItemCount() {
        return productList.size();
    }

    class ProductViewHolder extends RecyclerView.ViewHolder {

        TextView textviewisbn, textviewtitle, textviewauthors, textviewacc, textviewpublisher, textviewpubyear;

        ProductViewHolder(View itemView) {
            super(itemView);

            textviewisbn = itemView.findViewById(R.id.textviewisbn);
            textviewtitle = itemView.findViewById(R.id.textviewtitle);
            textviewauthors = itemView.findViewById(R.id.textviewauthors);
            textviewacc = itemView.findViewById(R.id.textviewacc);
            textviewpublisher = itemView.findViewById(R.id.textviewpublisher);
            textviewpubyear = itemView.findViewById(R.id.textviewpubyear);

        }
    }
}

当我运行我的应用程序时没有错误，但在调试选项卡上：价值：[{＆＃34; isbn＆＃34;：195472462，＆＃34; title＆＃34;：＆＃34; Oxford Practice Grammer＆＃34;，＆＃34;作者＆＃34;：＆＃34; john Eastwood＆＃34;，＆＃34;加入＆＃34;：1，＆＃34;出版商＆＃34;：＆＃34; Ameena Saiyid牛津大学＆＃34;，＆＃34; pubyear＆＃34;：2014，＆＃34 ;网页＆＃34;：432，＆＃34; RAK＆＃34;：1，＆＃34; HR＆＃34;：1，＆＃34; VR＆＃34;：1，＆＃34;条形码＆＃34 ;: 195472462}] 05-23 23:51:24.012 780-780 / com.desktop.app I / test：java.lang.NullPointerException：尝试调用接口方法＆＃39; boolean java.util.List.add（java.lang.Object ）＆＃39;在空对象引用上

我无法解析JSON以显示recylerview上的数据

0 个答案: